Ansible多主机执行故障：动态获取主机后无法调用变量

问题描述 #

我有一个分两部分执行的Ansible脚本：第一部分在localhost执行，查询数据库表以获取主机名；第二部分需要在之前查询得到的主机上运行。但第二部分无法使用第一部分中通过set_fact设置的主机变量。

原实现代码：

- hosts: localhost
  gather_facts: false
  become: yes
  become_user: oracle

  vars_files:
    - vars/main.yml

  tasks:
    - name: Get new hostname
      tempfile:
        state: file
      register: tf

    - name: create sql file
      template:
        src: get_hostname.sql.j2
        dest:"{{ tf.path }}"
        mode: 0775

    - name: login
      command:
        argv:
        - "sqlplus"
        - -s
        - "@{{ tf.path }}"
      environment: 
        ORACLE_HOME: "oracle/home"
      register: command_out

    - set_fact:
        NEW_HOST: "{{ command_out.stdout }}"

- hosts: "{{ NEW_HOST }}"
  gather_facts: false
  become: yes
  become_user: oracle

  vars_file:
    - vars/main.yml

  tasks:
    - name: debug
      command: hostname
      register: new_host_out

    - debug:
        msg: "new host is {{ new_host_out.stdout }}"

第一部分运行正常，但第二部分报错无法找到NEW_HOST变量。

问题原因 #

用set_fact设置的变量默认是当前Play目标主机的主机变量（此处为localhost），Ansible的不同Play之间不会自动共享主机变量，因此第二Play无法直接引用NEW_HOST。

解决方案 #

方案一：通过hostvars直接引用localhost的变量 #

修改第二Play的hosts字段，从localhost的主机变量中读取目标主机名：

- hosts: localhost
  gather_facts: false
  become: yes
  become_user: oracle

  vars_files:
    - vars/main.yml

  tasks:
    - name: Get new hostname
      tempfile:
        state: file
      register: tf

    - name: create sql file
      template:
        src: get_hostname.sql.j2
        dest:"{{ tf.path }}"
        mode: 0775

    - name: login
      command:
        argv:
        - "sqlplus"
        - -s
        - "@{{ tf.path }}"
      environment: 
        ORACLE_HOME: "oracle/home"
      register: command_out

    - set_fact:
        NEW_HOST: "{{ command_out.stdout | trim }}"  # 去除输出中的换行/空格

- hosts: "{{ hostvars['localhost'].NEW_HOST }}"
  gather_facts: false
  become: yes
  become_user: oracle

  vars_files:  # 修正原代码语法错误：vars_file → vars_files
    - vars/main.yml

  tasks:
    - name: debug
      command: hostname
      register: new_host_out

    - debug:
        msg: "new host is {{ new_host_out.stdout }}"

注意事项：

• 给command_out.stdout添加| trim过滤器，避免SQL输出的换行或多余空格导致主机名识别失败
• 修正第二Play中的vars_file为vars_files（原代码的语法错误）

方案二：使用add_host将主机添加到临时Inventory #

在第一Play中用add_host把获取到的主机添加到临时组，第二Play直接针对该组执行任务：

- hosts: localhost
  gather_facts: false
  become: yes
  become_user: oracle

  vars_files:
    - vars/main.yml

  tasks:
    - name: Get new hostname
      tempfile:
        state: file
      register: tf

    - name: create sql file
      template:
        src: get_hostname.sql.j2
        dest:"{{ tf.path }}"
        mode: 0775

    - name: login
      command:
        argv:
        - "sqlplus"
        - -s
        - "@{{ tf.path }}"
      environment: 
        ORACLE_HOME: "oracle/home"
      register: command_out

    - name: Add target host to temporary group
      add_host:
        name: "{{ command_out.stdout | trim }}"
        groups: temp_target_hosts  # 自定义临时组名称

- hosts: temp_target_hosts
  gather_facts: false
  become: yes
  become_user: oracle

  vars_files:
    - vars/main.yml

  tasks:
    - name: debug
      command: hostname
      register: new_host_out

    - debug:
        msg: "new host is {{ new_host_out.stdout }}"

该方案更直观，适合后续需要针对目标主机执行多组任务的场景，临时组可重复调用。

内容的提问来源于stack exchange，提问作者Yashwanth Veeranki